1. Field of the Invention
This invention relates to electronic systems, and more particularly, to systems for ensuring the proper powering up of those systems.
2. Description of the Related Art
While some integrated circuits may receive power from a single power supply, other integrated circuits (ICs) may receive power from multiple power supplies. Often times, ICs will have different voltage and/or current requirements for various types of circuitry such as drivers, receivers, core circuitry, phase-locked loops (PLLs) and so forth.
Powering up an IC receiving power from only a single power supply may be a relatively straightforward process. However, when multiple power supplies provide power to an IC, powering up may require power to be applied to the various circuits in a specific sequence. Failure to apply power in the proper sequence may result in the damage or destruction of various individual circuits of the IC.
Even when damage to circuitry is not a concern, a failure to apply power in the proper sequence to an IC may prevent it from functioning correctly. Many types of ICs (such as microprocessors) are required to enter a reset state and then proceed through an initialization sequence before they can perform their intended functions. The initialization sequence may include certain units of the IC exchanging information with other units that receive power from a different power supply. If one of the units involved in the attempted information exchange is not fully powered up, the information exchange will not occur, and the IC will not initialize properly.